Gearing



Nov. 16 1926,

A. w. GRIFFITH GEARING Filed August 1. 1923 2 Sheets-Sheet 1 Nov. 16,1926. 1,606,759

A. W. GRIFFITH GEAHING Filed August 1, 1923 2 sheets-shew. 2

l5 l Y 3 4 5 4,

CTI

laatented Nov. 16, 1926i.

stares PATENT QFFlfE.

GRIFFTE, OF PITTSBURGH, FENNSYLVANA; FRANCES GREFEITH, EX- ECUTSIX OF THE SAID ALBERT VJ'. GRIFFTH, DECESED, ASSG-'NOR TO GRllTI-I PATENTS COMPANY, OF PITTSBURGH, PENNSYLVANIA, A CORPORATIN OF DELA- *WARE GEARIN G.

Application leid August 1, 1923. Serial No. 655,024.

rEhe present invention relates broadly to caring and more particularly to that type f Gearing ordinarily referred to as' worm e aring, although the present invention posesses some of the desired attributes both of vo 'm gears and spiral gears.

@ne of the object-s of the present invention is to provide a construction particularly adapted for the eflicient transmission of power between non-parallel non-intersecting shafts` such gearing being especially useful in automotive vehicles as a drive between the propeller shaft and rear axle.

f* t the present time, it is customary in a number of automotive vehicles to utilize was CU worm gearing for transmitting power to the rear axle. Gearing of this character provides a powerful drive and permits the desired gear ratio to be easily obtained. Certain objections to this type of gearing have arisen, however, due to the projection for substantially a. full diameter of the worm beyond the periphery of the wormavheel. rlhis materially reduces the amount of clearance between the top of the differential housing and the body of the vehicle, thereby necessitating a special form of spring suspension.

It has heretofore been proposed, as illustrated, for example, in the patent to Fowler, No. 493,493 of March 14, 1893, to provide modified forms of worm gearing'in which the worm occupies a position within the periphery and laterally of the worm wheel. From a practical standpoint, however, con-v structions of this character as heretofore designed have not only been inefficient, but have been substantially inoperative for the purpose intended by reason of the disregard of certain inherent defects in the utilization of a worm having a constant helix angle.

The present invention also has for one of` its objects, the substantial elimination of the spreading force which is usually present in worm gearing and tending to deflect the worm wheel shaft. ln accordance with this invention, the spreading force is directed substantially axially of the shaft andany tendency to bend the same is thereby eliminated. y l l In the accompanying drawings, I have shown for purposes of illustration only, one embodiment of this invention, it being un- Figure 3 is a side elevationof the worm shown in Figure 1; and

Figure l is a transverse sectional view through a portion of the construction shown in Figure 1 on the plane of the line lV-l As before pointed out, thepreferred e1n- Y bodiment of my invention comprises a. con struction in which the teeth are formed on one of the side faces of the worm-wheel and in which the axis of the worm extends at substantially right angles to the axis of the worm wheel and in a different plane, whereby non-parallel non-intersecting axes are secured, the axis of' the worm preferably extending across the tooth face of the worm wheel to position the worm laterally of and substantially within the periphery of the wheel. It is with reference to a construction of this general character that the following description is applicable. y

ln carrying out the present invention, l preferably first determine the desired pitch line of the proposed worm wheel and the diameter of the worm tobe used therewith. This pitch line may then be represented by a circle L, as indicated in Figure 1.V The axis W ofthe worm is then drawn tangent to the pitch line L. The circumference of the worm may then be ascertained and a quarter of this circumference laid olf on each side of the axis W, as indicated by lines C and C. The distance between the lines C and C will obviously represent half the circumference of a developed worm so that there may be indicated between these lines the developed helix ll having a helix angle A, which angle is dependent upon the number of teeth originally selected for the worm wheel. The developed helix H is drawn through the point of tangency T between minates in the lines C and C at L andV /t respectively. p Y

laines perpendicular' to the axis oty the Worin are drawn through it and it and the distance between. their intersections z5 and t Vwith the pitch line L represents the distance moved by a tooth on the Worm Wheel in a halt revolution of the Worm. 'This linear distance is expressed on the` diagram as 12 l), the Vcorresponding angular distance turned through by the AWorin Wheel being represented as D.

Ubviously, any other peint on the pitch line L, as, roi-'example t2, must move through an equal angle D during a half revolution of the Worin, and if an e'liicient geel' `h-Vlflg i long life is to be'secured, the vvorm must be in contact -with the point t2 throughout this haltl revolution. It then, the point 152 is projected upwardly to C in the point 7b2 While the point t, which is the other limit of the angle D', is projected to the line C in the point h3, a line H connecting the points h2 and 7i? Will represent the proper helix line :tor this portion ofthe Worin. The corresponding pitch is represented on the diagram as /Q P and will be seen to vary considerably 'from thecriginally determined pitch at the center ot' the Worm. The correspendingvariation in the helix angle may be termed the helix angle departure and is represented by a shaded area on the diagram. Gbviously, if the original helix angle A Were maintained for this portion of the Worm, the tendency would beto turn 'the Worm wheel through an angle larger ,than the angle D or D', the diiterence being expressed by a shaded area on the diagram, designated error it helix angle A is maintained.

lt will be apparent that the above procedure may be carried outV for very small portions .oi3 the Worin and for very small angles corresponding to D, and in this manner 'theV proper helix angle from end to end of the Worm may be determined. lt Will be tound that the helix angle constantly varies from the Voriginally determined angle When this practice is pursued and a suitable worinV may be readily determined. Obviously, the gear ratio is determined by the ratio of the number o1e teeth on the Worm to the number ot teeth on the Wheel and any number oit' threads or teeth may be used Yon the Worm, as desired. As soon as one is determined, the others, which are, of course, identical, may be laid otlJ a suitable distance around the axis of the vvorm.

The proper Worm having thus been determined, aV suitable tooth shape'may be se# lected and the tvorm cutV in accordanee'there- With. Such a Worm may be formed Yinto ya heb Vand used to generate the Worm wheel in a gear cutting machine, as is Well known.

Figures 2 and illustrate a` Worm and vheel constructed according to my invention.- Here a Worm Wheel 2 having teeth 8 on oneside 'tace thereotis shown in engagement with a )vorm 1l carried by a shait is will be seen from Figure 3, the outline ot the Worm departs from the usual cylindrical vform and is slightly convex. l have found that this form enables me to provide a longer Worm Without interference.

Figure et shows a partial section taken 'through the Worm and Worm Wheel and illustrates clearly the positioning ot' the teeth 8 with respect to the Worm Wheel d. .itvvill be seen that a line 6 drawn through the center of the Worm 4t and parallel to the axis of the Worm Wheel 2 approximately divides thejpitch lineV 7 oit the tooth Obviously, each tooth 5 maybe extended on either side of the line 6, but the pitch line 7 Will be substantially symn etrieal about the line 6. Preferably, the line 6 bisects the pitch "line 7. i

ln the gearing illustrated, the Worm l has six threads and the Worm Wheel 2 has twenty-nine teeth. Dynamometer tests made with this gear have shown etiiciencies ot' v94% at 1700` R. P. M At this speed.V

the eliiciency remains the same `tor practically all loads Within the capacity ot thegear. Correspondingly high eli'iciencies were found at all the speeds under varying load conditions. As my invention may be embodied in a reversible gearing, as in the illustrated form, the utility ot the Y, invention for automotive Work vvill be apparent.

Gearing constructed according vtothis invention islvery compact and may be placed in a housing of smaller diameterthan an ordinary Worm of the same load capacity. lhe two shafts are closer togetherr andthe housing may, therefore,` be made lighter While preserving the same or greater rigidity. f

rlhe spreading torce kordinarily tending to flex the Worm Wheel shaft is not present in this drive since the spreading torce between the teeth is exert-ed longitudinally of thek Worm Wheel shaft. In certain types ot drive, this may be of considerable,advan-. tage since the shaft need only be strongV enough to carry the load Without the ilexing and distortion ordinarily set .up in` Worm Wheel drives.

The advantages of the present arise `from the provision ot an improved gearing insuring both the necessary strength andcrigidity in a more compact form.

Further advantages of the invention arise from the provision of a gearing in which thel v'vorm is laterally disposed With respect to the Worin vvheel and in which a line passF ing through the axis oi' the Worm and exinvention lll) lil() llO tending parallel to the axis of the worm wheel passes through and preferably -intersects a tooth on the worm wheel.

Still further at vantages of the invention arise from the provision of a gearing particularly adapted for non-parallel nonintersecting shafts in which t-he principal point of contact between the gears lies outside of the shortest line connecting the shafts of the two gears, or such line projected.

l claim:

l. ln worm gearing, a worm wheel haviixed teeth of generally spiral form on one side face thereof, and a. worni'disposed laterally of said wheel and having a tooth adapted to mesh with the teeth on said wheel, said worm having a varying helix angle, and being adapted to make surface Contact with a plurality of teeth on the wheel at all times.

Q. In worin gearing, a worm wheel having fixed teeth of generally spiral form on one side face thereof, and a worin disposed laterally of said wheel and having a tooth adapted to mesh with the teeth of said wheel, said worin having a constantly changing helix angle, and being adapted to make surface Contact with a plurality of teeth on the wheel at all times.

3. A worin and gear connection for nonpa-rallel non-intersecting shafts, having its principal point of contact lying outside the shortest line connecting the two shafts or such line projected, the worm wheel having fixed teeth of generally spiral form, the worin being adapted to make surface. contact with a plurality of teeth on the wheel at all times.

4t. A worm and gear connection for non` parallel non-intersecting shafts having its principal point of contact lying outside the shortest line connecting the two shafts or such line projected, the wheel having fixed teeth of generally spiral form and the worin being adapted to make surface contact with a plurality of teeth on the wheel at all times. i

5. In a worm gearing, aY worm wheel having fixed teeth of generally spiral form on a side face thereof, the pitch line of each of said Ateeth being substantially sy1mnetrical about a line parallel to the axis of rota tion of the wheel, and a worm disposed laterally of said wheel and having a substantially continuous and uninterrupted tooth adapted to mesh with the teeth of said wheel, said worm having a changing helix angle.

6. As an article of manufacture, a worin convex from end to end and provided with a tooth having a varying helix angle.

7. As an article of manufacture, a worin convex from end to end and provided with a tooth having a constantly changing helix angle.

S. As an article of manufacture, a worin convex from end to end and provided with a tooth having a helix angleA increasing from leach end toward the center.

ln testimony whereof I have hereunto set my hand.

ALBERT w. GRirFrrH. 

